1. Field of the Invention
The present invention relates to a transmission for a vehicle wherein hydraulic clutches are provided between a crankshaft and main shafts of an power unit, each hydraulic clutch being put into a connected state by adjustment of oil pressure therein, and wherein a plurality of selectively connectable speed-stage gear trains are provided between a transmission output shaft and the main shafts in such a manner that a neutral condition can be obtained.
2. Description of the Background Art
A conventional transmission for a vehicle includes a plurality of speed-stage gear trains divided into two groups. In the transmission, two hydraulic clutches are used to achieve individual changeover of connection and disconnection of power from a crankshaft to both groups of gear trains. The two hydraulic clutches are controlled so that one of the hydraulic clutches is put into a disconnected state when the other is in a connected state, and both of the hydraulic clutches are put into the disconnected state in a neutral condition, where no gear train is engaged. A conventional transmission of this type is disclosed, for example, in Japanese Patent Laid-Open No. 2005-273829.
However, in the transmission disclosed in Japanese Patent Laid-Open No. 2005-273829, at the time of an engaging operation of a starting gear train for making a transition from a neutral condition to a starting condition, an oil pressure is applied to the hydraulic clutch corresponding to the starting gear train to thereby put the hydraulic clutch into the connected state. Therefore, when the oil pressure acts on the hydraulic clutch, even though the hydraulic clutch is not in a perfect connected state, a speed change shock is generated due to drag of the hydraulic clutch.
The present invention has been made in consideration of the above circumstances. Accordingly, it is an object of the present invention to provide a transmission for a vehicle in which a speed change shock is not generated at the time of starting from a neutral condition.